Based in Berkshire near London we have more than 15 years experience supplying & installing flue systems and chimney breasts across the whole of Southern England. Our fitters are all Hetas or Gas Safe Registered. We fit flexible flue liner and twin wall flue systems along with false chimney breasts.
If your chimney is already lined (say with clay or concrete) then legally, as long as your flue is sound then this is right. However, fitting a liner with a stove is not just about the legal question it’s as much to do with the performance and maintainability of your stove.
Say your open fire is about 10% efficient, and a stove is 80% efficient. This is directly related to how much hot flue gases are produced. The stove by design, exhausts far less hot flue gases than an open fire. For a flue to work correctly the temperature inside the flue must be hotter than outside the flue.
If the flue lining does not get hot then you risk excessive condensation (creating creosote) and a poor draw. A flue liner sets the size of the flue ideally for the stove. Years ago we used to design and make stainless steel adapters between fireplaces with clay or concrete liners and stoves to save fitting a liner but allow the flue to be swept through the stove they never last! Sooner or later they will leak creosote or come adrift, they not a good solution unless there is no other choice.
If your clay liner is 9 and your stove pipe is 5 without removing the stove its not possible to sweep the flue properly. Some large old chimneys designed to pull on a large open fire can pull so hard that it is not possible to control the stove properly, a liner helps to correct this.
In the end, the informed advice is that you are wasting your time and money buying a good stove and fitting it without a good quality liner.
“I have been told that I do not need to have a flue liner”
Flexible Flue Liner
A flexible flue liner is designed for re-lining an existing masonry chimney. Flexible flue liners are manufactured with two skins of stainless steel 316 L or 904L and are suitable for gas, oil and multi-fuel, including wood burning appliances where the maximum flue gas temperature does not exceed 600°C.
Why do you need a flexible flue liner?
There are three principle reasons you may need a chimney liner:
- Because your chimney has no clay tile chimney liner (older chimneys may not)
- The clay tile chimney liner is damaged
- A chimney liner is required for optimal performance and safety because you are installing a new heating unit (stove or furnace) that will be vented into your masonry chimney.
What does a flue liner do?
Chimney liners and flue liners are stainless steel liners which, when installed into a masonry chimney, produce a continuous and unbroken flue from appliance or fire to outlet. This prevents flue gasses escaping though disintegrating brickwork and provides the optimum flue diameter for the appliance.
What are the benefits?
Installation – Flexible liners are easier to install than the rigid variety. The single length of flexible liners makes it easier to fit into the chimney.
Versatility -The adjustable length of flexible liners is great for taller chimneys or chimneys that may have contours or even just slight bends.
Less Creosote – Flexible flue liners accumulate less creosote than the rigid flue liners, especially when used on wood fireplaces and stoves. The flexing process loosens the creosote and causes it to fall off.
Easier Maintenance – One of the factors that create regular chimney cleaning and maintenance work is the accumulation of creosote. Flexible liners prevent much buildup of creosote.
Higher Safety – Installing a flexible liner is a great way of minimizing the risk of a chimney fire.
Improves Chimney Draft – Less buildup of creosote from a flexible liner improves the chimney draft. This enhances chimney efficiency.
Adds to Home Value – The various benefits of flexible flue liners improve chimney efficiency. An efficient chimney is a significant consideration in home valuation.
How long do flue liners last?
The answer to this question depends on the type of chimney liner you have.
Clay tile liners and cast in place liners – Typically last around 50 years.
Stainless steel flue liners – Generally last for 15 to 20 years (though low quality liners may not even last for five).
Twin Wall Flue
Twin wall flue pipe is a metal tube (flue) insulated with approx. an inch of insulation (two layers of stainless steel with insulation between). Stainless and black powder coated systems are fully interchangeable. The insulation is necessary to keep the gases hot.
How does a twin wall flue work?
Twin wall flue systems are used with a stove when it is fitted into a property where there is no masonry chimney. It can run internally or externally and it achieves higher temperatures due to the layer of insulation. You cannot use single wall flue pipe in place of twin wall flue pipe.
Why do you need a twin wall flue?
If you need to exit the room, whether out through a wall or through a ceiling then you must use twin wall flue pipe and then stay with twin wall flue pipe to the cowl (unless going into a chimney higher up). Twin wall flue pipe should always be kept a minimum of Xcm from any combustible materials.
What are the benefits?
The benefits are that you can heat the flue quicker when lighting the stove, improving the draw and getting the stove up to temperature quicker. Not so important if you have the stove lit all day, however if you are only lighting it for a few hours at night, it would be a benefit.
By using a twin wall insulated flue system, an existing chimney is no longer required to be fitted in the flue system and the stove can be easily installed almost anywhere you want. A twin wall flue pipe is usually a system of two layers stainless steel pipes having about 25mm of insulation tightly sandwiched between them.
Since the chimney is no longer needed while using a twin wall flue pipe, flues can be easily installed, maintained and manoeuvred through a wall or ceiling. If the area does not have an existing chimney, then this type of flue pipe is eminent for appliances using oil, wood or any other solid fuel.
All appliances having a twin wall flue pipe system are placed at the apex which is the topmost point of the roof. If not done so, there could be a down draft resulting in pushing the smoke back to the stove and all inside the room causing serious discomfort to the user.
There are no real benefits to having twinwall over single skin flue pipe other than the safety aspects / aesthetics . Most twinwall has a minimum distance to combustibles of between 50-70mm so generally it is much easier to meet these requirements vs single skin pipe (3 x diameter of pipe – minimum distance to combustibles). Single skin pipe can be secured in the same way as twinwall can (with clamps and wall brackets) and will be considerably cheaper.
Does twin wall flue get hot?
Your twin wall flue should have a label with it which will show the distance to combustibles on it. … Twin wall flue can get hot enough on the outside so that you would not want to keep your hand on it for very long but will not normally get much hotter than that so you might not think this is too much of a problem.